1. Field of the Invention
This invention pertains in general to a non-volatile memory device and, more particularly, to a method of forming a gate oxide on a polysilicon floating gate with improved surface roughness through chemical metal polishing.
2. Description of the Related Art
In a non-volatile memory device, the integrity of the dielectric layer that separates a floating gate from a control gate mainly determines the leakage and breakdown characteristics of the memory device. The dielectric layer, commonly known as a gate oxide, is formed by oxidation where a layer of silicon dioxide SiO.sub.2 is grown on a polysilicon layer in an oxygen-rich environment at an elevated temperature. During the oxidation process, the integrity of the gate oxide is partly determined by the roughness of the surface on which the gate oxide is grown. Other factors such as oxidation conditions also influence the integrity of the gate oxide.
A rough polysilicon surface is undesirable because such surface roughness leads to high local electric fields that disrupt device operations and obstructs the formation of a strong gate oxide layer during the oxidation process. The effect of a polysilicon layer having a rough surface becomes more evident in memory devices scaled down to sub-micron applications.